Movable support for abrading apparatus

ABSTRACT

A nozzle for directing an abrasive stream and a workpiece holder are adjustably positioned relative to one another in horizontal directions by means of device which supports one or the other by horizontal slide structures that are movable at right angles to each other.

United States Patent Inventor Walter Kulischenko East Brunswick, NJ.

Appl. No. 831,825

Filed June 6, 1969 Patented July 20, 1971 Assignee Pennvvalt CorporationPhiladelphia, Pa.

MOVABLE SUPPORT FOR ABRADING APPARATUS 2 Claims, 5 Drawing Figs.

U.S.Cl ..51/8,51/l4, 51/217, 269/56 int. Cl B24c 3/12 FieldoiSearchS1/8,9, 14,

[56] References Cited UNITED STATES PATENTS 1,849,384 3/1932 Ruemelin51/8 3,101,574 8/1963 West 51/217X 3,425,166 2/1969 Best et al. 51/14Primary Examiner-Lester M. Swingle Attorneys-Carl A. Hechmer, Jr. andEdward A. Sager ABSTRACT: A nozzle for directing an abrasive stream anda workpiece holder are adjustably positioned relative to one another inhorizontal directions by means of device which supports one or the otherby horizontal slide structures that are movable at right angles to eachother.

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A T TORNE Y MOVABLE SUPPORT FOR ABRADING APPARATUS This inventionrelates to abrading apparatus, especially abrading apparatus of the typewherein an abrasive stream issuing from a nozzle is employed fortrimming miniature electrical resistors of circuits printed onnonconductive substrates. More particularly,- the invention relates toan improvement in the supporting structure of the apparatus whichpermits the workpiece holder and the nozzle to'be movably'positionedrelative to one another in horizontal directions prior to the abradingoperation.

Abrading apparatus of the type described is usually provided withseparate supports for the workpiece holder and the trimming headincluding the nozzle. The nozzle is pointed downwardly toward the uppersurface of the workpiece where the'workpiece is secured. Conventionally,it is a tedious procedure to loosen. and then retighten various bolts ofthe supports when aiming the nozzle as part of the initial setup for thefirst slide structure. Preferably the second slide structure system ispressurized. In order to achieve uniform cutting action the apparatus isarranged to provide a uniform concentration of particles in a'constantairstream issuing from the nozzle at about 40 to 80 p.s.i.

The supply conduit 14 may be flexible hose of abrasion resistantmaterial at the end of a length of rigid tubing, and it is preferredthat the terminal or end portion adjacent the nozzle 12 be of rigidtubular construction so that it can serve as nozzle holder 26 capable ofhaving its movements accurately controlled by a traversing mechanism 28connected thereto by a rigidly constructed arm 30. The nozzle holder 26is suitably journaled in the extended free end of the arm 30, in uprightposition above a support 32 for the workpiece 10. The support 32 ismounted on a base 33. The traversing mechanism 28 may also be mounted ona support 32, mounted in turn on the base 33. The mechanism 28 serves tomove the nozzle 12 in horizontal direction by its holder 26, transverseto the longitudinal extent of the holder, or into and out of the placeof the drawing illustrating the apparatus, whereby the abrasive streamis traversed along the length of the workpiece to cut or ab'rade alongthe line of travel. The traversing mechanism 28 responds to signalsreceived via conductors 34 from a control 36 to move a controlleddistance first in one direction and then usually in opposite or reversedirection upon completion of an abrading operation. The control 36 alsosends energizing comprises slides connected to the opposite ends of thefirst slide structure and mounted on respective spaced and parallelbars. The first slide structure may be constructed similar to the Isecond slide structure, although they are movable at right angles to oneanother within substantially the same horizontal plane.

Thev invention will now be described in greater detail with referenceto. the drawings, in which:

I FIG; 1 is an isometric view of a movable support constructed accordingto theinvention;

FIG. 2 is a vertical sectional view of the same, taken along line 2-2 ofFIG. 1;

FIG. 3 is a horizontal sectional view of the same, taken along line 3-3of FIG. 2; 7

FIG. 4 is a diagrammatic illustration of abrading apparatus in which themovable support of FIG. 1 is incorporated; and

FIG. 5 is an enlarged plan view of a miniature resistor which can betrimmed by the apparatus of FIG. 4.

Before describing the movable support of FIG. 1 to 3, the abradingapparatus as a whole illustrated in FIG. 4 and the workpiece of FIG. 5will be described.

The abrading apparatus is applied to the trimming of a thick-filmresistor or other workpiece designated generally by the numeral 10,utilizing a high velocity abrasive stream issuing from a nozzle l2. Thelatter is supplied through a supply I conduit 14 by a mixing chamber 16where dry, filtered, pressurizedair at about 85.p.s.i. from a compressor18 is uniformly mixed in thedesiredproportions with abrasive powder froma reservoir 20.- By means of a unique arrangement more fully describedin the present inventors application Ser. No.

365,] 23, filed May 5, 1964, now US. Patent No. 3,344,524, a

vibrator 22 is employed to apply vibrations to the chamber 16.

' This arrangement can produce an automatically replenished trickleofaabout 3 to 5 grams per minute of aluminum oxide or other. abrasivepowder having'an average particle size of 27 microns, from the reservoir20 through a passageway (not shown yto the mixing chamber 16 forcombining with the pressurized'air.

- The" flow of airborne. abrasive particles is initiated'by theenergizationof a solenoid operated pinch valve 24in the upstream endofthe supply conduit 14, that is, at the outlet of the mixingchamber 16.The nozzle 12 wilhhave a restricted orifice; e.g. 0.0l8inch diameter, ofmuch smaller cross-sectional flow area than the supply conduiti 14 ,andthus the entire current through conductors 38 to the'solenoid of pinchvalve 24 to effect its closing upon completion of an abrading operation;but otherwise during abrasive trimming the pinch valve 24 is held open.

The workpiece 10 shown in FIG. 5 is an electrical resistor having athick, electrically resistive film 40 printed on a nonconductivesubstrate and having a pair of terminals 42 joined to opposed paralleledges thereof. As shown, the resistor 10 has been trimmed between thelines designated by the letters A and C. The trimmed area lying betweenlines B and C represents the amount of the film 40 trimmed byovershooting during the elapsed time between issuance of the signal tostop and the actual point of stopping. Broken line D represents thepoint at which abrasive flow ceases during reverse movement of thenozzle.

Referring again to FIG. 4, a pair of probes 44 are connected duringtrimming between terminals 42 and control 36 by conductors' 48 so thatthe electrical resistance of the resistor 10 can be continuouslymonitored by the control 36 as work proceeds. v j

The vibrator 22 may be connected as shown to the control 36 byconductors 46. The concentration'of abrasive particles in the abrasivejet can be set by adjusting the amplitude of vibrations applied to themixing. chamber in direct relation to the desired abrasive capability ofthe jet since the cutting action of the abrasive stream corresponds tothe abrasive concentration:

Accordingly, the electrical resistor 10is trimmed by directing a jet ofairborne abrasive particles toward the film 40 at close range, whilemoving the jet at constant forward speed across part of the surface ofthe film in a path between the terminals 42 so as to reduce itscross-sectional area. While moving the jet the increasing resistance ofthe resistor 10 is continuously measured and the additional timerequired to further increase resistance to the desired value can beprojected, so that the film material remaining has the desiredelectrical resistance within a high degree of accuracy. With forwardnozzle travel speeds of I inch per minute, resistor values within plusor minus one-tenth percent can be achieved without difficulty. Withtrimming speeds up to 6 inches per minute, accuracy within three-tenthspercent can be obtained; and where less accuracy is required, trimmingspeeds can be increased to and beyond 15 inches per minute.

For maximum accuracy, trimming should be accomplished by moving thenozzle, not only at constant forward speed, but a constant distancebetween the nozzle 12 and the film 40.

The control 36 may incorporate a 4-wire resistance limit bridge,integral to the electrical control system, for monitoring the resistoras it is being trimmed and sending a signal to the pinch valve 24 and tothe traversing mechanism 28 in the manner and at the time described.

Although the apparatus has been described as applied to the trimming ofelectrical resistors, the invention is also applicable to the trimmingof other kinds of electrical elements such as capacitors. Therefore, theapparatus can be employed whether trimming effects an increase ordecrease in the electrical value being measured.

Although not shown, the workpiece can be mounted on a support 32 whichincludes a clamping device affording quick, secure and easy insertionand removal of the workpiece. The present invention is directlyconcerned with an adjustably movable support 32 for the workpiece 10,but the same construction may be used for the support 32 for themechanism 28. Either or both supports 32 may be made as in FIG. 1 to 3,whereby the nozzle 12 and the workpiece 10 are horizontally movablerelative to one another during the initial set up and then locked inplace for repeated use on a number of similar workpieces.

The movable support 32 of FIG. 1 to 3 includes a horizontal mountingplate 50 having holes 52 for securing the plate to the base 33. It alsoincludes four upright corner posts 54 fixed to the plate 50, as byscrews 56, and extending upwardly therefrom. Rigidly supported by theposts 54 above the plate 50 are a pair of widely spaced, parallel bars58. The bars 58 are of uniform circular cross section and they extendhorizontally. Setscrews 60 secure the bars 58 at their end portions tothe corner posts 54.

Slidablymounted on the respective bars 58 are horizontally elongatedslide blocks 62 and 63 having a horizontal passageway extendinglongitudinally passageway of block 62 is fitted with a ball bushing 64which snugly receives the bar 58 in rolling contact to ensure smooth andstraight movement of the block on the bar with a minumum of friction.The ball brushing 64 is secured in position by retaining rings 66engaging the wall of the passageway at opposite ends of the bushing. Afelt washer 68 encircles the bars 58 outwardly of each bushing 64 andprovides a seal for the passageway.

The other slide block 63 is preferably provided with a ball plunger 70and locking screw 72 with a knurled head, arranged on the opposite sidesof the bar 58 for locking the block 63 to that bar. For this block 62and the ball bushings 64 may be disposed in a passageway thereof onopposite sides of the lock screw 72, and further provided with retainingrings 66 and felt washers 68.

Connected between the slide blocks 62 and 63 is horizontally elongatedslide structure 74, The slide structure 74 is movable with the slideblocks 62 and 63 in a first horizontal directions on the bars 58,although the slide structure is elongated in a second horizontaldirection which is at right angles to the direction of movement on thebars 58.

The slide structure 74 comprises a pair of closely spaced bars 76similar in construction to the bars 58 and disposed in the samehorizontal plane with them. The bars 76 are at right angles with thebars 58, however. The ends of the bars 76 are received in sockets in theslide blocks 62 and 63 and secured by screws 78.

therethrough. The 7 The slide structure 74 further includes slide blocksand 82 which are slidably mounted on the bars 76 and joined by a coverplate 84 with screws 86 for unitary movement.

The slide block 80 is structurally similar to the slide block 62previously described. Therefore, a description thereof will not berepeated, and like reference numerals are employed to designatecorrespondingly similar parts of the blocks 62 and 80.

Likewise, the slide blocks 82 and 63 are structurally alike, and againlike reference numerals are used to designate correspondingly similarparts thereof without descriptive repetitlon.

As will be apparent from the drawings, the movable portion 80, 82 and 84of the slide structure 74 is movable in one horizontal direction withthe slide blocks 62 and 63, and it is also movable in another horizontaldirection between the slide blocks 62 and 63. The two horizontaldirections are at right angles to each other. Furthermore, the slidebars 58 and 76 are in substantially the same horizontal plane in orderto minimize the overall vertical dimension of the support 32.

The cover plate 84 is suitable for mounting either a workpiece 10thereon, as with an appropriate clamping device (not shown), or forcarrying the traversing mechanism 28 in the general manner shown.

In operation, assuming the support 32 to be under a workpiece 10, thelock screws 72 are turned outwardly to disengage them from theirrespective slide bars. When unsecured the slide blocks 62 and 63 and theslide structure 74 are freely movable in a wide horizontal range withinthe edges of the mounting plate 50 for positioning the workpiece l0 andthe nozzle 12 relative to one another prior to abrading the resistivefilm 40. Once positioned as desired, the lock screws 72 are turnedinward to secure the blocks 62 and 63 and the slide structure 74, andabrading operations may be started.

lclaim:

1. ln abrading apparatus, the combination with a first assemblycomprising a vertical nozzle adapted to direct a pressurized abrasivestream toward a workpiece, means for supplying said pressurized abrasivestream to said nozzle, and a stationary support therefor, of a movablesupport having a horizontally flat surface for supporting said workpiecebeneath said nozzle, said movable support being adapted to initiallyposition said workpiece with respect to said nozzle, said movablesupport including a base mounted to said stationary support a first pairof spaced and parallel bars carried by said base and extending in afirst horizontal direction, first slides mounted on the respective firstpair of bars for sliding movement in said first horizontal direction,horizontally elongated slide structure extending between said slides,said slide structure including a second pair of spaced and parallel barsextending in a second horizontal direction at a right angle to saidfirst pair of bars, second slides mounted on the respective second pairof bars for sliding movement in said second horizontal direction, and alocking screw carried by at least one of each set of slides and beingengageable with the bar associated therewith for locking said movablesupport against movement.

2. The combination described in claim 1, wherein each of said pairs ofbars is disposed in substantially the same horizontal plane.

1. In abrading apparatus, the combination with a first assemblycomprising a vertical nozzle adapted to direct a pressurized abrasivestream toward a workpiece, means for supplying said pressurized abrasivestream to said nozzle, and a stationary support therefor, of a movablesupport having a horizontally flat surface for supporting said workpiecebeneath said nozzle, said movable support being adapted to initiallyposition said workpiece with respect to said nozzle, said movablesupport including a base mounted to said stationary support a first pairof spaced and parallel bars carried by said base and extending in afirst horizontal direction, first slides mounted on the respective firstpair of bars for sliding movement in said first horizontal direction,horizontally elongated slide structure extending between said slides,said slide structure including a second pair of spaced and parallel barsextending in a second horizontal direction at a right angle to saidfirst pair of bars, second slides mounted on the respective second pairof bars for sliding movement in said second horizontal direction, and alocking screw carried by at least one of each set of slides and beingengageable with the bar associated therewith for locking said movablesupport against movement.
 2. The combination described in claim 1,wherein each of said pairs of bars is disposed in substantially the samehorizontal plane.